CN113646184A

CN113646184A - Tyre crown reinforcement consisting of two working crown layers

Info

Publication number: CN113646184A
Application number: CN202080025004.9A
Authority: CN
Inventors: O·富尼耶; S·诺埃尔
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 2019-03-29
Filing date: 2020-03-24
Publication date: 2021-11-12
Anticipated expiration: 2040-03-24
Also published as: WO2020200923A1; BR112021018344A2; EP3946972B1; CA3132257A1; FR3094278A1; EP3946972A1; FR3094278B1; CN113646184B

Abstract

The present invention relates to a tyre of the heavy vehicle type intended to be mounted on a hollow rim of the 15 ° deep well type. According to the invention, only two working crown layers (41, 42) are present over at least 40% of the width (L5) of the tread (5) for forming the crown reinforcement (4), the absolute value of the difference between the absolute values of the angles α 2 and α 1 being greater than 4 DEG, α 2 being greater than α 1 in absolute value, the average angle α satisfying the relation 20+164 × exp (-L/100)<α<23+164 × exp (-L/100), the reinforcing elements of the carcass reinforcement (2) being of less than 20cm in a test called the air permeability test³Flow of/minAn amount of unencapsulated cord within which the rubber compound is present.

Description

Tyre crown reinforcement consisting of two working crown layers

Technical Field

The present invention relates to a tire having a radial carcass reinforcement, and more particularly to a tire intended to be mounted to a vehicle carrying heavy loads (such as a truck, tractor, trailer or bus).

Background

In tires of the heavy type, the carcass reinforcement is usually anchored on both sides in the bead region and is surmounted radially by a crown reinforcement consisting of at least two superposed layers formed by threads or cords which are parallel in each layer and crossed from one layer to the next, forming an angle of between 10 ° and 45 ° with the circumferential direction. The working layer forming the working reinforcement may also be covered with at least one layer, called protective layer, formed of reinforcing elements, advantageously metallic and extensible, and called elastic reinforcing elements. It may also comprise a layer of metal wires or cords forming an angle of between 45 ° and 90 ° with the circumferential direction, this ply being called a triangular ply and being radially located between the carcass reinforcement and the first crown ply, called the working ply and formed by parallel wires or cords laid at an angle not exceeding 45 ° in absolute value. The V-ply forms, with at least said working ply, a V-reinforcement having little deformation under the various stresses to which it is subjected, said V-ply serving substantially to absorb the transverse compressive forces exerted on all the reinforcing elements in the crown region of the tyre.

Cords are said to be inextensible when they exhibit a relative elongation at most equal to 0.2% under a tensile force equal to 10% breaking force.

A cord is said to be elastic when it exhibits a relative elongation at least equal to 3% and a maximum tangent modulus less than 150GPa, under a tensile force equal to the breaking load.

The circumferential reinforcing elements are reinforcing elements forming an angle in the range +2.5 ° to-2.5 ° (relative to 0 °) with the circumferential direction.

The circumferential direction or longitudinal direction of the tire is a direction corresponding to the outer periphery of the tire and defined by the running direction of the tire.

The transverse or axial direction of the tire is parallel to the axis of rotation of the tire.

The radial direction is a direction intersecting with and perpendicular to the axis of rotation of the tire.

The axis of rotation of a tire is the axis about which the tire rotates in normal use.

A radial or meridian plane is a plane containing the axis of rotation of the tire.

The circumferential mid-plane or equatorial plane is a plane perpendicular to the axis of rotation of the tire and dividing the tire in two halves.

For metal wires or cords, the force at break (maximum load in N), the strength at break (in MPa), the elongation at break (total elongation in%) and the modulus (in GPa) were measured under tension according to standard ISO 6892 of 1984.

Due to improvements in road networks and the expansion of global highway networks, some tires, which are today referred to as "road tires", are intended to travel longer and longer distances at high average speeds. The combined conditions required for such tire travel certainly enable an increase in the covered distance, since the tires wear less. This increase in life in terms of distance covered, coupled with the fact that such service conditions may lead to relatively high crown temperatures under heavy loads, indicates the need to increase the endurance of the tire crown reinforcement at least proportionally.

This is because there are stresses in the crown reinforcement, more specifically shear stresses between the crown layers, which, in the event of an excessive increase in the operating temperature at the ends of the axially shortest crown layer, lead to the appearance and propagation of cracks in the rubber at said ends. The same problem exists in the case of the edges of two layers of reinforcing elements, the other layer not necessarily being radially adjacent to the first layer.

In order to improve the endurance of the crown reinforcement of a tire, french application FR 2728510 proposes: in one aspect, an axially continuous ply is provided between the carcass reinforcement and the working ply of the crown reinforcement radially closest to the rotation axis, said axially continuous ply being formed by inextensible metal cords forming an angle with the circumferential direction at least equal to 60 °, and having an axial width at least equal to the axial width of the shortest working crown ply; between the two working crown plies, on the other hand, an additional ply is provided, formed by metallic elements oriented substantially parallel to the circumferential direction.

Furthermore, french application WO 99/24269 proposes in particular that, on each side of the equatorial plane and in the immediate axial extension of an additional ply of reinforcing elements substantially parallel to the circumferential direction, two working crown plies (which are formed by reinforcing elements crossed from one ply to the next) are coupled over an axial distance and then uncoupled using profiled elements of rubber compound at least over the remaining width common to said two working plies.

Furthermore, the use of tires on heavy vehicles of the "jobsite supply" type means that the tires are subjected to impact loads when driving over a rocky ground. These impact loads are of course detrimental to the performance in terms of durability.

It is also known practice for the person skilled in the art to increase the number of plies constituting the crown reinforcement in order to improve the endurance of the tire with respect to these impact loads.

In all the solutions described above, the presence of one or more additional layers of reinforcing elements leads to greater tyre mass and higher tyre manufacturing costs.

From document WO 2017/149222, a tire is also known whose crown reinforcement is lightened, which improves the endurance of the tire with respect to these impacts. However, the inventors have found that the endurance performance of such tires may be reduced when running on ground that imposes significant stresses on the tires, for example under particularly severe running conditions combining vehicle speed, load to which the tires are subjected and ground properties. In fact, a reduction in endurance performance can be observed, for example, when running at relatively high speeds on ground of the type supplied at work sites where tyres are very demanding. Decelerating the vehicle may limit the risk of reduced endurance performance, but the driver experiences problems and at the cost of sacrificing vehicle productivity.

Disclosure of Invention

It is an object of the present invention to provide a tire for "heavy" vehicles (for example vehicles of the "field supply" type), in which the performance in terms of durability is further improved, irrespective of the nature of the ground and of the driving conditions, in particular with respect to the impact loads to which the tread is subjected, and the overall mass of the tire is limited.

According to the invention, this object is achieved by a tire for heavy vehicles intended to be mounted on a drop-in rim of the 15 ° drop-in type and having a radial carcass reinforcement consisting of at least one layer of reinforcing elements, the tire comprising a crown reinforcement comprising two working crown layers with reinforcing elements that cross from one layer to the other and form angles (α 1, α 2) of between 8 ° and 45 ° with the circumferential direction, the angles α 1 and α 2 being oriented on either side of the circumferential direction, the crown reinforcement being radially surmounted by a tread connected to two beads by two sidewalls, the two working crown layers being the only layers present over at least 40% of the axial width of the crown reinforcement to form the crown reinforcement, the reinforcing elements of the radially outermost working layer forming an angle α 2 with the circumferential direction that is greater in absolute value than the angle formed by the radially innermost working layer The reinforcing elements of the layers form an angle α 1 with the circumferential direction, the absolute value of the difference between the absolute values of the angles α 2 and α 1 being greater than 4 °, the average angle α satisfying the following relation:

20+164*exp(-L/100)<α<23+164*exp(-L/100)，

α is represented by the relational expression Arctan ((tan (| α 1 |). tan (| α 2|))^1/2) By definition, L is measured in the axial directionThe maximum width of the quantity of tyre and expressed in mm, the metal reinforcing elements of said at least one layer of carcass reinforcement being cords, preferably non-encapsulated cords, which, in a test known as the air permeability test, give rise to less than 20cm³A flow rate/min, a rubber compound being present at least locally within the structure of the cord.

A drop-in rim (15 deg. drop-in) or a safety humped drop-in rim within the meaning of the present invention is a one-piece rim as defined in ETRTO, wherein the seat intended to receive the tyre bead has a frustoconical shape forming an angle substantially equal to 15 deg. with the axial direction. These seats also extend through a rim flange of reduced height compared to the flange of a flat-bottomed rim (the rim seat of which has a substantially cylindrical shape).

The width L is measured in millimeters on a tire mounted on its nominal rim and inflated to its nominal pressure.

The angles α 1 and α 2 in degrees are measured on a cross section of the tire. According to the invention, the angle is measured at the circumferential mid-plane.

A test known as the permeability test makes it possible to determine the longitudinal permeability of a test curtain to air by measuring the volume of air that passes through the test specimen over a given period of time and at a constant pressure. As is well known to those skilled in the art, the principle of this test is to prove the effectiveness of the treatment of the cord to render it impermeable; it has been described, for example, in the standard ASTM D2692-98.

This test was performed on cords drawn directly from the vulcanized rubber ply by peeling, which cords reinforce the vulcanized rubber ply and are therefore penetrated by the cured rubber. According to the invention, the test portion of the cords is located in the crown region of the tire, i.e. the portion of the cords of the carcass reinforcement close to the tread.

The cord is therefore coated with a rubber compound (or coating rubber) in the cured state, this test being carried out on a 2cm length of said cord in the following manner: air is injected at the inlet end of the cord at a pressure of 1 bar and a flow meter (calibrated, for example from 0 to 500 cm) is used³/min) the volume of air at the outlet end was measured. During the measurement, a sample of the cord is fixed in a compressed airtight seal (for example a seal made of dense foam or rubber) so that only the amount of air passing through the cord from one end to the other along the longitudinal axis of the cord is considered in the measurement; the airtightness of the airtight seal itself was checked in advance using a solid rubber test specimen (i.e., a test specimen without a cord).

The lower the measured average air flow (average of 10 test specimens), the higher the longitudinal impermeability of the cord. Since the accuracy of the measurement is + -0.2 cm³Min is less than or equal to 0.2cm³The measured value of/min is considered zero; said measurement corresponds to the cord along its axis (i.e. in its longitudinal direction) which may be referred to as airtight (completely airtight).

This permeability test also constitutes a simple means of indirectly measuring the degree of penetration of the rubber composition into the cord. The lower the measured flow, the higher the degree of penetration of the rubber into the cord.

The degree of penetration of the cord can also be estimated according to the following method. In the case of a layered cord, the method consists in: in a first step, the outer layer is removed from the sample having a length of between 2 and 4cm, and then the sum of the lengths of the rubber compounds with respect to the length of the sample is measured in the longitudinal direction and along a given axis. The measurements of the length of the rubber compound do not include spaces along the longitudinal axis that are not penetrated. These measurements were repeated along three longitudinal axes distributed over the circumference of the sample, and the measurements were repeated over five cord samples.

When the cord comprises a plurality of layers, the first removal step is repeated for a new outer layer and the length of the rubber compound is measured along the longitudinal axis.

The average of all the proportions of the length of the rubber compound to the length of the sample thus determined is then calculated in order to determine the degree of penetration of the cord.

Also advantageously, the tyre according to the invention is intended to be inflated to an inflation pressure P greater than or equal to 6.5 bar.

Preferably, according to the invention, the reinforcing elements of the two working crown layers are made of metal.

The results obtained with the tyre according to the invention effectively demonstrate: particularly when driving over a rocky ground, the performance in terms of durability can be improved; and the crown reinforcement of the tire is lightened. The lightening of the crown reinforcement of the tire is accompanied by a simplification of the manufacturing process and a reduction of the manufacturing costs.

Unexpectedly, the results effectively show that the tire according to the invention can be lightened by reducing the number of layers constituting the crown reinforcement, while maintaining or even improving the endurance performance of the tire crown, irrespective of the ground properties and driving conditions, in particular with respect to the impact loads to which the tread is subjected.

In particular, the person skilled in the art knows that, in order to improve the endurance performance of the crown reinforcement of a tire with respect to this type of impact load, it is common practice to increase the number of layers of reinforcing elements.

The inventors believe that these results can be explained by the fact that: the angle formed by the reinforcing elements of the radially innermost working crown layer with the circumferential direction is smaller in absolute value than the angle formed by the reinforcing elements of the radially outermost working crown layer. They found that such a small angle seems to delay the absorption of the tensile force by the reinforcing element in the event of such an impact load. Generally, if the impact load is comparable to that observed when driving over a rocky ground, a fracture of the reinforcing element (if such a fracture occurs) is found in the radially innermost layer. These observations seem to indicate that, in the face of this type of attack, the angular difference of the reinforcing elements between the two working crown layers makes it possible to improve the endurance performance of the tire and at the same time to reduce the number of layers in the crown reinforcement.

The increased value of the average angle a compared to the more commonly known values for conventional tires used for such applications further improves the endurance performance of the tire crown with respect to the impact loads to which the tread is subjected. Such average angle alpha values are not generally used in such applications, in case they impair the durability of the carcass reinforcement, the reinforcing elements of which are subjected to excessively high compressive stresses.

However, the inventors have been able to demonstrate that the reinforcing elements of the carcass reinforcement according to the invention (which, in a test called the permeability test, yield less than 20 cm)³Flow/min, because of the presence of the rubber compound within the reinforcing element) exhibit compression characteristics allowing an average angle α according to the invention.

Advantageously according to the invention, the fracture potential index F2/FR2 of the radially outermost working layer is less than 1/6, wherein:

FR2 is the breaking force under uniaxial extension of the cords of the radially outermost working layer,

F2＝p₂*Tc*[(tan(|α1|)/((tan(|α1|)+tan(|α2|)))/cos²(|α2|)+C_F]wherein

Tc＝0.092*P*Rs*(1-(Rs²-R_L ²)/(2*Rt*Rs))，

P is the inflation pressure of the tire,

C_F＝0.00035*(min((L-80)/sin(|α1|),(L-80)/sin(|α2|),480)-480)，

p₂the pitch at which the reinforcing elements of the radially outermost working crown layer are laid, measured perpendicular to the reinforcing elements at the circumferential mid-plane,

Rs＝Re-Es，

re is the outer radius of the tire, measured at the radially outermost point on the tread surface of the tire, said surface being extrapolated to fill any voids that may be present,

es is the radial distance between the radially outermost point of the tyre and its orthogonal projection on the radially outer face of the reinforcing elements of the radially innermost working crown layer,

R_Lis the average of the radii of the axially outermost points of the main portion of the carcass reinforcement on each side of the tire,

rt is the radius of a circle passing through three points located on the outer surface of the tread outside the void and defined from the shoulder ends at axial distances 1/4, 1/2, and 3/4 equal to the axial width of the tread, respectively.

Thickness Es and pitch p₂Measured on a cross-section of the tyre and reported in mmShown in the figure.

The inventors have also observed that the choice of the absolute value of the difference between the absolute values of the angles α 1 and α 2 described above (angles α 1 and α 2 described above being associated with an average angle α and a fracture potential index F2/FR2, both as defined according to this advantageous embodiment of the invention) makes it possible to dispense with a protective layer generally mounted radially on the outside of the other layers of the crown reinforcement. There is generally a layer such that it can be sacrificed in the event of a cutting-type attack on the tyre, which can compromise the integrity of the metallic reinforcing element by corrosion phenomena associated with fatigue of the reinforcing element. The inventors have effectively observed that the reinforcing elements of the radially outermost working crown layer of the tyre according to the invention are subjected to less stress when the tyre is inflated or when it is used in normal running, than the reinforcing elements of the radially outermost working crown layer of a more conventional tyre; the more conventional tyres have a smaller angular difference in absolute value between the reinforcing elements of the different working layers, the reinforcing elements of the radially innermost working layer forming an angle greater than or equal in absolute value to the angle of the reinforcing elements of the radially outermost working layer, and the fracture potential index F2/FR2 is higher. The reinforcing elements of the radially outermost working crown layer of the tyre according to the invention therefore have a durability performance that is much better than that of more conventional tyres; thus, the present inventors have found that the protective layer can be omitted, thereby contributing to the lightening of the tire.

According to a preferred embodiment of the invention, the absolute value of the difference between the absolute values of the angles α 2 and α 1 is greater than or equal to 6 °, preferably greater than 9 °. According to this embodiment, and according to the explanations provided above, it is possible to further improve the endurance performance of the reinforcing elements of the radially outermost working layer and/or to further improve the performance of the tyre with respect to impact loads (such as those experienced when driving over a rocky ground).

It is also advantageous according to the invention that the fracture potential index F2/FR2 of the radially outermost working layer is less than 1/8. Such a fracture potential index F2/FR2 further contributes to improving the endurance performance of the reinforcing elements of the radially outermost working layer during use of the tire.

Preferably according to the invention, the fracture potential index F1/FR1 of the radially innermost working layer is less than 1/3, wherein:

FR1 is the breaking force under uniaxial extension of the cords of the radially innermost working layer,

F1＝p₁*Tc*[(tan(|α2|)/(tan(|α1|)+tan(|α2|)))/cos²(|α1|)+C_F]wherein

p₁The pitch of laying of the reinforcing elements for the radially innermost working crown layer is measured perpendicular to the reinforcing elements at the circumferential mid-plane.

Also preferably, the fracture potential index F1/FR1 of the radially innermost working layer is at least 30% higher than the fracture potential index F2/FR2 of the radially outermost working layer.

According to one embodiment of the invention, the reinforcing elements of the working crown layer are inextensible metal cords.

According to an advantageous embodiment of the invention, the two working crown layers are the only layers present over at least 60% of the axial width of the crown reinforcement, and more advantageously over at least 80% of the axial width of the crown reinforcement to form the crown reinforcement. These advantageous embodiments of the invention aim to lighten the tyre even further.

According to one preferred embodiment of the invention to optimize the thinning of the crown of the tire, the two working crown layers are the only layers present over the entire axial width of the crown reinforcement to form the crown reinforcement.

According to a preferred embodiment of the invention, the cords of the carcass reinforcement produce less than 10cm in a test called the air permeability test³Min, more preferably less than 2cm³Flow/min.

According to an advantageous embodiment of the invention, the metal reinforcing elements of at least one layer of the carcass reinforcement are cords having at least two layers (preferably non-encapsulated cords), at least one inner layer being coated with a layer consisting of a non-crosslinkable, crosslinkable or crosslinked rubber composition (preferably a rubber composition based on at least one diene elastomer).

The invention also proposes a tire for a heavy vehicle intended to be mounted on a drop-in rim of the 15 ° drop-in type and having a radial carcass reinforcement consisting of at least one layer of reinforcing elements, the tire comprising a crown reinforcement comprising two working crown layers of reinforcing elements that cross from one layer to the other and form angles (α 1, α 2) of between 8 ° and 45 ° with the circumferential direction, the angles α 1 and α 2 being oriented on either side of the circumferential direction, the crown reinforcement being radially surmounted by a tread connected to two beads by two sidewalls, the two working crown layers being the only layers present over at least 40% of the axial width of the crown reinforcement to form the crown reinforcement, the reinforcing elements of the radially outermost working layer forming an angle α 2 with the circumferential direction that is greater in absolute value than the reinforcing elements of the radially innermost working layer The piece forms an angle α 1 with the circumferential direction, the absolute value of the difference between the absolute values of the angles α 2 and α 1 being greater than 4 °, the average angle α satisfying the following relation:

20+164*exp(-L/100)<α<23+164*exp(-L/100)，

α is represented by the relational expression Arctan ((tan (| α 1 |). tan (| α 2|))^1/2) By definition, L is the maximum width of the tyre measured in the axial direction and expressed in mm, and the metal reinforcing elements of at least one layer of the carcass reinforcement are cords having at least two layers (preferably non-encapsulated cords), at least one inner layer being coated with a layer consisting of a non-crosslinkable, crosslinkable or crosslinked rubber composition (preferably a rubber composition based on at least one diene elastomer).

Within the meaning of the present invention, a metal cord comprising at least two layers, of which at least one inner layer is coated with a layer consisting of a non-crosslinkable, crosslinkable or crosslinked rubber composition, generates almost zero and therefore less than 20cm in the so-called air permeability test³Flow/min.

The expression "composition based on at least one diene elastomer" means, in a known manner, that the composition comprises predominantly (i.e. in excess of 50% by mass) this or these diene elastomers.

It should be noted that the covering according to the invention extends continuously around the layer it covers (i.e. it is continuous in the "orthogonal" direction of the cord perpendicular to its radius), so as to form a continuous sleeve, advantageously almost circular in cross-section.

It should also be noted that when the rubber composition of the covering is crosslinkable or crosslinked, it comprises, by definition, a crosslinking system suitable for causing the composition to crosslink during curing (even if the composition hardens rather than melts); thus, the rubber composition may be referred to as non-meltable because it cannot be melted by heating regardless of the temperature.

Preferably, the composition of this coating is chosen to be the same as that used for the rubber matrix to which the cord according to the invention is intended to reinforce. Thus, there is no problem of potential incompatibility between the respective materials of the covering and the rubber substrate.

According to one variant form of the invention, the reinforcing elements of at least one layer of the carcass reinforcement are [ L + M ]]Or [ L + M + N]A layered metal cord of construction and comprising a first layer C1 surrounded by at least one intermediate layer C2, the first layer C1 having L groups with a diameter d₁Wherein L ranges from 1 to 4, and the intermediate layer C2 has M filaments with a diameter d₂And at a lay length p₂Helically wound together filaments, wherein M ranges from 3 to 12, said layer C2 optionally being surrounded by an outer layer C3, the outer layer C3 having N filaments with a diameter d₃And at a lay length p₃Helically wound together wires, wherein N ranges from 8 to 20, and a coating consisting of a non-crosslinkable, crosslinkable or crosslinked rubber composition based on at least one diene elastomer, in [ L + M ]]In construction covering the first layer C1 and in [ L + M + N]Covering at least the layer C1 and/or at least the layer C2 in a construction.

Preferably, the diameter of the filaments of the first layer of the inner layer (C1) is between 0.10 and 0.5mm and the diameter of the filaments of the outer layer (C2, C3) is between 0.10 and 0.5 mm.

Also preferably, said filaments of the outer layer (C3) are wound with a helical lay length comprised between 8 and 25 mm.

Within the meaning of the invention, the lay length denotes the length measured parallel to the cord axis, at the end of which a thread with this lay length completes one full turn around the cord axis; thus, if the axis is sectioned by two planes perpendicular to said axis and separated by a length equal to the lay length of the filaments of the layer forming the cord, the axis of the filament has the same position in these two planes on the two circles corresponding to the layer of filaments in question.

Generally, said metal cords of at least one layer of the carcass reinforcement according to the invention can be made using any type of metal wires, in particular wires made of steel, for example wires made of carbon steel and/or stainless steel wires. Carbon steel is preferably used, but of course other steels or other alloys may be used.

Said metal cords of at least one layer of the carcass reinforcement according to the invention can be obtained by various techniques known to the skilled man, for example in two steps, initially passing through the extrusion head cladding C1 or the core or intermediate L + M structure (layer C1+ C2), this step being followed in a second step by a final operation of stranding or twisting the M + N filaments of layers C2 and C3 around the previously clad layer C1 or the N filaments of layer C3 around the previously clad layer C2.

According to a further alternative form of embodiment of the invention, which compensates the tyre performance compromise in a less profitable way in terms of mitigation, the crown reinforcement comprises an additional layer, called protective layer, radially on the outside of the working crown layer, preferably centred on the circumferential mid-plane. The reinforcing elements of such a protective layer are preferably reinforcing elements, known as elastic reinforcing elements, which are oriented at an angle of between 8 ° and 45 ° with respect to the circumferential direction and are in the same direction as the angle formed by the reinforcing elements of the radially adjacent working layer. It is also preferred that the reinforcing elements of such a protective layer are parallel to the reinforcing elements of the working layer radially adjacent thereto.

Other variants can also be provided as follows: the crown reinforcement is supplemented between the carcass reinforcement and the radially inner working layer closest to the carcass reinforcement by a triangular layer made of inextensible steel metal reinforcing elements forming an angle greater than 45 ° with the circumferential direction and having the same direction as the angle formed by the reinforcing elements of the layer radially closest to the carcass reinforcement. Advantageously, the triangular layer is made up of two half-layers, which are located axially on both sides of the circumferential mid-plane.

Drawings

Further details and advantageous features of the invention will become apparent from the description of exemplary embodiments of the invention given hereinafter with reference to the accompanying drawings, which show a meridian view of a drawing of a tyre according to one embodiment of the invention.

For ease of understanding, the drawings are not drawn to scale.

The figures show only half of the view of the tyre, which extends symmetrically about an axis XX', which represents the circumferential mid-plane or equatorial plane of the tyre.

Detailed Description

In the figures, a tyre 1 of size 385/65R 22.5 comprises a radial carcass reinforcement 2, said radial carcass reinforcement 2 being anchored in two beads (not shown in the figures). The carcass reinforcement 2 is formed by a single layer of metal cords. Which further comprises a tread 5.

The reinforcing elements of the layers of the carcass reinforcement 2 are non-encapsulated layered cords of 1+6+12 structure, consisting of a central core formed by one thread, an intermediate layer formed by six threads and an outer layer formed by twelve threads.

They have the following characteristics (d and p in mm):

-structure 1+6+ 12;

-d₁＝0.20(mm)；

-d₂＝0.18(mm)；

-p₂＝10(mm)；

-d₃＝0.18(mm)；

-p₃＝10(mm)；

-(d₂/d₃)＝1；

wherein d is₂And p₂Respectively the diameter and the helical lay length of the intermediate layer, and d₃And p₃The diameter of the filaments and the helical lay length of the outer layer, respectively.

The core of the cord, consisting of a central core formed by one thread and an intermediate layer formed by six threads, is coated with a rubber composition based on an unvulcanized diene elastomer (in an untreated state). The sheathing is achieved by means of an extrusion head of the core, followed by a final operation of 12 filaments twisted or cabled around the thus sheathed core to form the outer layer.

In a test called the permeability test, the flow generated by the cords is equal to 0cm³Min, thus less than 2cm³And/min. The permeability of the rubber composition is greater than 98%.

The cords have a diameter equal to 0.95 mm.

The elastomer composition constituting the rubber coating is made of the composition as described above.

In the figures, the carcass reinforcement 2 is hooped according to the invention by a crown reinforcement 4, said crown reinforcement 4 being formed radially from the inside outwards by:

a first working layer 41 formed by metal cords oriented at an angle equal to 12 °,

a second working layer 42 formed of metal cords oriented at an angle equal to 43 ° and crossed with the metal cords of the first working layer 41, the cords of each of the working

layers

41, 42 being oriented on each side in the circumferential direction.

The metal cords constituting the reinforcing elements of the two working layers are cords of the gauge 9.35. They are distributed in each working layer with a distance between the reinforcing elements equal to 2mm, measured in a direction perpendicular to the bisector of the cord.

The tire was inflated to a pressure of 9 bar.

Axial width L of first working layer 41₄₁Equal to 280 mm.

Axial width L of second working layer 42₄₂Equal to 260 mm.

Axial width L of tread₅Equal to 303 mm.

The axial width L is equal to 377 mm.

The combined mass of the two working layers 41, 42 (including the mass of the metal cords and the skin compound) thus amounts to 9.1 kg.

The difference between the angle formed by the cords of the first working crown layer and the circumferential direction and the angle of the cords of the second working crown layer is equal to 31 °.

The average angle is equal to 24 °, obviously between 23.8 ° and 26.8 °.

Re was measured equal to 536.9 mm.

The measured value of Es equals 24.9 mm.

Average value R of measured radii_LEqual to 409 mm.

The value Rt determined on the tyre is equal to 1400 mm.

The calculated value of Tc is equal to 359.9N/mm.

C_FIs equal to 0.

The value of F1 is equal to 673.9N.

The value of F2 is equal to 274.8N.

The breaking forces FR1 and FR2 of the reinforcing elements of the working crown layer are equal to 2600N.

The fracture potential index F2/FR2 is equal to 10.6%.

The fracture potential index F1/FR1 equals 25.9%.

The fracture potential index F1/FR1 is 145% higher than the fracture potential index F2/FR 2.

Comparing the tyre I according to the invention with a reference tyre R1 of the same dimensions, this reference tyre R1 differs from the tyre I according to the invention in the nature of the reinforcing elements of the carcass reinforcement on the one hand. The reinforcing elements of the carcass reinforcement of this first reference tire R1 were non-encapsulated layered cords of 1+6+12 structure (same as the cords of tire I according to the invention), the core of which was not coated with a rubber composition.

Such cords produce a flow equal to 40cm in a test called the air permeability test (as described above)³And/min. The permeability of the rubber composition is equal to 66%.

The first reference tire R1 also differs from the tire I according to the invention in that its crown reinforcement is formed radially from the inside towards the outside by:

a second working layer 42 formed of metal cords oriented at an angle equal to 40 ° and crossed with the metal cords of the first working layer 41, the cords of each of the working

layers

41, 42 being oriented on each side in the circumferential direction.

The tire was inflated to a pressure of 9 bar.

Axial width L of first working layer 41₄₁Equal to 280 mm.

Axial width L of second working layer 42₄₂Equal to 260 mm.

Axial width L of tread₅Equal to 303 mm.

The axial width L is equal to 377 mm.

The difference between the angle formed by the cords of the first working crown layer and the circumferential direction and the angle of the cords of the second working crown layer is equal to 28 °.

The average angle is equal to 22.9 °.

Re was measured equal to 536.9 mm.

The measured value of Es equals 24.9 mm.

Average value R of measured radii_LEqual to 409 mm.

The value Rt determined on the tyre is equal to 1400 mm.

The calculated value of Tc is equal to 395.9N/mm.

C_FCalculated value of-0.01.

The value of F1 is equal to 655.3N.

The value of F2 is equal to 267.7N.

The fracture potential index F2/FR2 is equal to 10.3%.

The fracture potential index F1/FR1 is equal to 25.2%.

The tyre I according to the invention is also compared with a second reference tyre R2 of the same dimensions, said second reference tyre R2 being different from the first reference tyre R1 in that its crown reinforcement is formed radially from the inside towards the outside by:

-a triangular layer formed by metal cords oriented at an angle equal to 50 °,

a first working layer formed of metal cords oriented at an angle equal to 18 ° with respect to the circumferential direction on the same side as the cords of the triangular layer,

-a second working layer formed of metal cords oriented at an angle equal to 18 ° and crossed with respect to the metal cords of the first working layer, the cords of each of the working layers being oriented on both sides in the circumferential direction,

-a protective layer formed by elastic 6.35 metal cords, wherein the distance between the reinforcing elements measured along a direction perpendicular to the bisector of the cords is equal to 2.5mm, said elastic 6.35 metal cords being oriented at an angle equal to 18 ° on the same side as the cords of the second working layer.

The metal cords of the two working layers and the triangular layer are cords of the gauge 9.35. They are distributed in each working layer with a distance between the reinforcing elements equal to 2.5mm, measured in a direction perpendicular to the bisector of the cords.

The reference tire was inflated to a pressure of 9 bar.

The axial width of the triangular layers is equal to 260 mm.

The axial width of the first working layer is equal to 280 mm.

The axial width of the second working layer is equal to 260 mm.

The axial width of the protective layer is equal to 200 mm.

The combined mass of the working, protective and triangular layers of the reference tire (including the mass of the metal cords and the skin compound) amounted to 14.1 kg.

The absolute value of the difference between the absolute value of the angle formed by the cords of the first working crown layer and the circumferential direction and the absolute value of the cords of the second working crown layer is zero, i.e. the angles are the same, unlike the present invention.

The average angle is equal to 18.

The value of F1 is equal to 600N.

The value of F2 is equal to 523N.

The values of F1 and F2 were obtained by finite element simulation, the large number of reinforcement plies in the crown making it impossible to use a simple analytical model.

The fracture potential index F2/FR2 is equal to 20.1%.

The fracture potential index F1/FR1 equals 23.1%.

The fracture potential index F1/FR1 is 15% higher than the fracture potential index F2/FR 2.

Tests were carried out using tire I according to the invention and reference tires R1 and R2.

A first endurance test was carried out on a testing machine driving each tire in a straight line at an initial load of 3550daN equal to the maximum speed class (speed index) specified for the tire, which was gradually increased in order to reduce the duration of the test.

Other durability tests were conducted on a testing machine that periodically applied lateral loads and dynamic overloads to the tire. The tires according to the invention were tested under the same conditions as applied to the reference tire.

The tests carried out thus show that the distance covered by the tyre according to the invention and the reference tyre is substantially the same in each test. It is therefore evident that the performances of the tire according to the invention in terms of endurance of the crown reinforcement when running on an asphalt surface are substantially equivalent to those of the reference tire.

Tests aimed at characterizing the breaking strength of the crown reinforcement of a tire subjected to impact loading were also carried out. These tests consist of running the tire over a cylindrical obstacle or dimpling tool of diameter equal to 1.5 inches (i.e. 38.1mm) and of a given height, inflating the tire to the recommended pressure and subjecting it to the recommended load. The breaking strength is characterized by the critical height of the dimpling tool, which is also the maximum height of the dimpling tool that results in complete failure of the crown reinforcement (i.e. failure of all the crown layers). These values represent the energy required to break the crown block. These values are represented with reference to a base 100, said base 100 corresponding to the value measured for the reference tyre R2.

Reference R2	100
		Reference R1	108
Invention I	114

These results show that, despite the lightening of the tire (in particular by reducing the mass of the crown reinforcement), the energy at break in the case of impact loading of the tread surface is significantly higher than that of the reference tire R2. A comparison of the results between the tire according to the invention and the reference tire R1 shows that it is possible to increase significantly the energy required for the crown block to break without compromising the durability of the layer of carcass reinforcement, even if it is subjected to higher stresses in terms of the compressive load on the reinforcing elements. These results clearly demonstrate that the presence of the rubber compound in the reinforcing elements confers on them compression characteristics allowing an average angle a according to the invention which is favorable to the endurance performance of the crown reinforcement of the tyre.

Another tire according to the present invention, I2, was tested. This tire I2 differs from tire I in the reinforcing element properties of the layer of carcass reinforcement. The reinforcing elements of this layer of carcass reinforcement of tire I2 were non-encapsulated layered cords of 1+6+11 structure consisting of a central core formed by one filament, an intermediate layer formed by six filaments and an outer layer formed by eleven filaments.

They have the following characteristics (d and p in mm):

-structure 1+6+ 11;

-d₁＝0.20(mm)；

-d₂＝0.175(mm)；

-p₂＝7(mm)；

-d₃＝0.175(mm)；

-p₃＝10(mm)；

-(d₂/d₃)＝1；

The core of the cord, which is composed of the central core portion formed of one filament and the intermediate layer formed of six filaments, is not coated with the rubber composition.

Such cords produce a flow equal to 5cm in a test called the air permeability test (as described above)³And/min. The permeability of the rubber composition is equal to 98%.

In tests intended to characterize the breaking strength of the crown reinforcement of a tire, the amount of energy required to break the crown block is expressed with reference to the base 100 (corresponding to the value measured for the reference tire R2) and is equal to 114.

Claims

1. Tyre (1) for heavy vehicles, the tyre (1) being intended to be mounted on a drop-well rim of the 15 ° drop-well type and having a radial carcass reinforcement (2) consisting of at least one layer of reinforcing elements, the tyre comprising a crown reinforcement (4), the crown reinforcement (4) comprising two working crown layers (41, 42) having reinforcing elements which cross from one layer to the other and form, with the circumferential direction, angles (α 1, α 2) between 8 ° and 45 °, the angles α 1 and α 2 being oriented on either side of the circumferential direction, the crown reinforcement (4) being radially surmounted by a tread (5) connected to the two beads by two sidewalls, characterized in that:

-the two working crown layers (41, 42) being the only layers present over at least 40% of the axial width of the crown reinforcement (4) to form the crown reinforcement (4),

-the angle (α 2) formed by the reinforcing elements of the radially outermost working layer (42) with the circumferential direction is greater in absolute value than the angle (α 1) formed by the reinforcing elements of the radially innermost working layer (41) with the circumferential direction,

-the absolute value of the difference between the absolute values of angles (α 2) and (α 1) is greater than 4 °,

the average angle α satisfies the following relation:

20+164*exp(-L/100)<α<23+164*exp(-L/100)，

α is represented by the relational expression Arctan ((tan (| α 1 |). tan (| α 2|))^1/2) By definition, L is the maximum width of the tire measured in the axial direction and is expressed in mm,

-the metal reinforcing elements of at least one layer of the carcass reinforcement are of less than 20cm in the so-called air permeability test³A flow rate per min, and

-at least locally a rubber compound is present within the structure of the cord.

2. Tyre (1) according to claim 1, characterized in that the fracture potential index F2/FR2 of the radially outermost working layer is less than 1/6, wherein:

F2＝p₂*Tc*[(tan(|α1|)/((tan(|α1|)+tan(|α2|)))/cos²(|α2|)+C_F]wherein

Tc＝0.092*P*Rs*(1-(Rs²-R_L ²)/(2*Rt*Rs))，

P is the inflation pressure of the tire,

C_F＝0.00035*(min((L-80)/sin(|α1|),(L-80)/sin(|α2|),480)-480)，

Rs＝Re-Es，

re is the outer radius of the tire, measured at the radially outermost point on the tread surface of the tire, said surface being extrapolated to fill any voids present,

R_Lis the average of the radii of the axially outermost points on each side of the tire,

rt is the radius of a circle passing through three points on the outer surface of the tread outside the void and defined at axial distances from the shoulder ends equal to 1/4, 1/2, and 3/4, respectively, of the tread width.

3. Tyre (1) according to claim 1 or 2, characterized in that the reinforcing elements of said two working crown layers (41, 42) are made of metal.

4. Tyre (1) according to claim 1 or 2, characterized in that the absolute value of the difference between the absolute values of the angles α 2 and α 1 is greater than or equal to 6 °, preferably greater than 9 °.

5. Tyre (1) according to any one of claims 1 to 4, characterized in that the fracture potential index F2/FR2 of the radially outermost working layer (42) is less than 1/8.

6. Tyre (1) according to any one of claims 1 to 5, characterized in that the fracture potential index F1/FR1 of the radially innermost working layer (41) is less than 1/3, wherein:

F1＝p₁*Tc*[(tan(|α2|)/((tan(|α1|)+tan(|α2|)))/cos²(|α1|)+C_F]wherein

7. Tyre (1) according to claim 6, characterized in that the fracture potential index F1/FR1 of the radially innermost working layer (41) is at least 30% higher than the fracture potential index F2/FR2 of the radially outermost working layer (42).

8. Tyre according to any one of the preceding claims, characterized in that the two working crown layers (41, 42) are the only layers present over the entire axial width of the crown reinforcement (4) to form the crown reinforcement.

9. Tyre (1) according to any one of the preceding claims, characterized in that at least one layer of the carcass reinforcement (2) results in less than 20cm in a test called the air permeability test³The metallic reinforcing elements of flow/min are cords comprising at least two layers, and at least one inner layer is coated with a layer consisting of a polymer composition, such as a non-crosslinkable, crosslinkable or crosslinked rubber composition, preferably based on at least one diene elastomer.

10. Tyre (1) according to any one of the preceding claims, characterized in that the metal cords of at least one layer of the carcass reinforcement (2) produce less than 10cm in a test called the air permeability test³Min, more preferably less than 2cm³Flow/min.

11. Tyre (1) for heavy vehicles, the tyre (1) being intended to be mounted on a drop-well rim of the 15 ° drop-well type and having a radial carcass reinforcement (2) consisting of at least one layer of reinforcing elements, the tyre comprising a crown reinforcement (4), the crown reinforcement (4) comprising two working crown layers (41, 42) having reinforcing elements which cross from one layer to the other and form, with the circumferential direction, angles (α 1, α 2) between 8 ° and 45 °, the angles α 1 and α 2 being oriented on either side of the circumferential direction, the crown reinforcement (4) being radially surmounted by a tread (5) connected to the two beads by two sidewalls, characterized in that:

the average angle α satisfies the following relation:

20+164*exp(-L/100)<α<23+164*exp(-L/100)，

α is represented by the relational expression Arctan ((tan (| α 1 |). tan (| α 2|))^1/2) By definition, L is the maximum width of the tire measured in the axial direction and is expressed in mm, and

the metal reinforcing elements of at least one layer of the carcass reinforcement are cords comprising at least two layers, at least one inner layer being coated with a layer consisting of a polymer composition, for example a non-crosslinkable, crosslinkable or crosslinked rubber composition, preferably based on at least one diene elastomer.

12. Tyre according to any one of the preceding claims, characterized in that the reinforcing elements of at least one layer of the carcass reinforcement are [ L + M [ ]]Or [ L + M + N]A layered metal cord of construction and comprising a first layer C1 surrounded by at least one intermediate layer C2, the first layer C1 having L groups with a diameter d₁Wherein L ranges from 1 to 4, and the intermediate layer C2 has M filamentsDiameter d₂And at a lay length p₂Helically wound together wires, where M ranges from 3 to 12, the layer C2 being able to be surrounded by an outer layer C3, the outer layer C3 having N filaments with a diameter d₃And at a lay length p₃Helically wound together wires, wherein N ranges from 8 to 20, and a coating consisting of a non-crosslinkable, crosslinkable or crosslinked rubber composition based on at least one diene elastomer, in [ L + M ]]In construction covering the first layer C1 and in [ L + M + N]Covering at least the layer C1 and/or at least the layer C2 in a construction.